call

  1. Function.prototype.myCall = function(context) {
  2.   if (typeof this !== 'function') {
  3.     throw new TypeError('Error')
  4.   }
  5.   context = context || window
  6.   context.fn = this
  7.   const args = [...arguments].slice(1)
  8.   const result = context.fn(...args)
  9.   delete context.fn
  10.   return result
  11. }

apply

  1. Function.prototype.myApply = function(context) {
  2.   if (typeof this !== 'function') {
  3.     throw new TypeError('Error')
  4.   }
  5.   context = context || window
  6.   context.fn = this
  7.   let result
  8.   // 处理参数和 call 有区别
  9.   if (arguments[1]) {
  10.     result = context.fn(...arguments[1])
  11.   } else {
  12.     result = context.fn()
  13.   }
  14.   delete context.fn
  15.   return result
  16. }

bind

  1. Function.prototype.myBind = function (context) {
  2.   if (typeof this !== 'function') {
  3.     throw new TypeError('Error')
  4.   }
  5.   const _this = this
  6.   const args = [...arguments].slice(1)
  7.   // 返回一个函数
  8.   return function F() {
  9.     // 因为返回了一个函数，我们可以 new F()，所以需要判断
  10.     if (this instanceof F) {
  11.       return new _this(...args, ...arguments)
  12.     }
  13.     return _this.apply(context, args.concat(...arguments))
  14.   }
  15. }